Vapor compression heat pump systems are widely used to provide heating and cooling air conditioning to residential and, to a lesser extent, commercial facilities. One drawback of the vapor compression heat pump systems is that the heating capacity decreases as the ambient temperature decreases. Thus, during winter months the vapor compression heat pump systems lack efficiency. Moreover, with low ambient temperatures, building heat losses increase such that building temperatures decrease. One well-known solution to the inefficiency problem has been the addition of auxiliary electric heat strips. Unfortunately, the heat strips increase power usage and therefore system cost.
In recent years, combination air conditioner/heat pump systems have been suggested as a solution to the inefficiencies discussed above. A gas engine driven air conditioner/heat pump system utilizes a natural gas engine, instead of a traditional electric motor, to drive a compressor in the refrigerant circuit. An air conditioner/heat pump system utilizing a natural gas engine is known as a gas heat pump type air conditioner (“GHP”). The GHP uses natural gas, which is less expensive compared to other fuels such that the operating cost of the GHP is less than air conditioner/heat pump system driven by a conventional electric motor (“EHP”).
One advantage of using a combustion type engine, in lieu of an electric motor, in a heat pump system is the ability to use excess heat of combustion generated by the engine. The excess heat is available for wintertime heat augmentation thereby reducing or eliminating the need for auxiliary heaters. It has been a common practice with combustion engine heat pump systems to recover the excess heat from the engine by conveying a working fluid (e.g., water and ethylene glycol antifreeze) through the cooling and sometimes the exhaust system such that waste heat from the engine is absorbed by the working fluid. The heated working fluid is then pumped to a heat exchanger or radiator located in the air flow leading to the air-conditioned space.
Another advantage of using a combustion engine is the significant reduction is costs associated with the use of inexpensive fuel sources such as natural gas, propane and similar gaseous fuels.
While the advantages of using waste heat from a combustion engine are well recognized, the wide range of options for recovering and using the waste heat has required numerous, separate components to facilitate the heat exchange, auxiliary heating, defrosting and heat rejection. The complexity, size and cost of the heat pump systems having desirable heat recovery and use capability have increased accordingly. In addition, the use of small internal combustion engines at high ambient temperatures and at increased altitudes is problematic in that the environmental conditions reduce output horsepower.
Therefore, the need exists for a heat pump system which recovers and applies wasted heat effectively into the air-conditioned space and minimizes the use of electrical power demand and costs during both the heating and cooling heat pump cycles in high temperature environments.